Why silicone hydrogel is the contact lens material of choice

Since being introduced almost 20 years ago, silicone hydrogel (SiHy) contact lenses have become the predominant lens choice of eye care professionals. SiHy lenses have practically eliminated the hypoxia-related effects of hydrogel lenses.

In 2015, 81% of US patients were fitted with SiHy lenses rather than traditional hydrogel lenses.1

The first SiHy daily disposable sphere lens was introduced in 2008. This technological breakthrough was quickly succeeded by the introduction of SiHy daily disposables for sphere, toric and multifocal prescriptions.2

SiHy lenses have a higher Dk/t than hydrogel lenses, so SiHy wearers generally do not experience the effects of limited corneal oxygen supply. These can include:2

Corneal swelling

Epithelial microcysts

Refractive error changes and corneal distortion

Limbal hyperemia

Corneal vascularisation

In addition to oxygen transmissibility, eye care professionals recommending SiHy lenses to current hydrogel wearers may want to note potential cosmetic benefits. In studies, eye care professionals have noted increased visibility of reddened blood vessels and decreased corneal clarity in wearers of hydrogel lenses versus non-wearers of contact lenses.3,4 On the other hand, they found there was no observable difference between wearers of SiHy lenses and non-wearers.5

Many eye care professionals have assumed that hydrogel lenses must be less comfortable than SiHy lenses due to their higher modulus. The literature on this is inconclusive, as both the study design and the widely varying bulk properties of particular lenses can have a major impact on study findings. It is still unclear how much modulus affects any potential comfort differences between hydrogel and SiHy.6,7

However, studies have shown that subjective measures of comfort do improve when patients switch from hydrogel to SiHy lenses. Other factors instead of or in addition to modulus, such as oxygen transmissibility or edge design, may be responsible.6

SiHy lenses offer high oxygen transmission, a number of cosmetic and comfort benefits, and are available in a wide range of prescriptions, all of which combine to recommend them as the standard contact lens material of choice over hydrogel.2